In recent years, various electronic devices have been downsized made light-weight, and yet sophisticated. This market trend also requires downsizing of push-on switches to be used in operating sections of the electronic devices.
A conventional push-on switch is described hereinafter with reference to FIG. 8-FIG. 10. FIG. 8 is a sectional view of the conventional push-on switch, and FIG. 9 is an exploded perspective view of the conventional push-on switch. FIG. 10 is a sectional view illustrating the conventional push-on switch depressed. Housing 1 is made of synthetic resin and includes an opening at the top face. On a recessed inner bottom face of housing 1, there are center fixed contact 2 made of metal and two outer fixed contacts 3 made of metal and disposed symmetrically relative to center fixed contact 2. In other words, center fixed contact 2 is interposed between the two outer fixed contacts 3. Terminal 2A connected to center contact 2 and terminal 3A connected to outer fixed contacts 3 are led outside housing 1.
Movable contact 4 is made of an elastic thin metal plate and forms a dome bowing upward. The underside of movable contact 4 is surface-treated for good electrical conductivity. Movable contact 4 is accommodated in the recess of housing 1, and a lower end of the rim of movable contact 4 is seated on outer fixed contacts 3. The center section of the underside of movable contact 4 faces the top face of center fixed contact 2 with a space therebetween.
Protective sheet 5 is formed by applying pressure-sensitive adhesive (not shown) onto the underside of an insulating film, and protective sheet 5 is fixed on housing 1 with the adhesive such that sheet 5 can cover the top face of the recess of housing 1.
The conventional push-on switch is constructed as discussed above. The operation of this switch is described hereinafter. First, depressing force is applied from above protective sheet 5 to the center section of domed (bowing upward) movable contact 4, and when the depressing force exceeds a given level, the center section of movable contact 4 elastically reverses (protruding downward or bowing downward) with tactile click-feel as shown in FIG. 10. Movable contact 4 then touches center fixed contact 2 with the center section of the underside of movable contact 4. Outer fixed contacts 3 become electrically conductive to center fixed contact 2 via movable contact 4, so that terminals 2A and 3A corresponding respectively to center contact 2 and outer contacts 3 are placed into a switch-on state.
When the depressing force is removed, the center section of movable contact 4 elastically restores to the original shape, i.e. bowing upward, with tactile click-feel, and movable contact 4 leaves center fixed contact 2 at the center of the underside of movable contact 4. The terminals 2A and 3A are thus placed in a switch-off state.
Prior art related to the present invention includes Japanese Patent Unexamined Publications No. 2003-297175 and No. 2002-63823.
Housing 1 of the foregoing conventional push-on switch is formed by insert-molding the center fixed contact 2, outer fixed contacts 3, and terminals 2A and 3A together, where terminals 2A and 3A correspond to contact 2 and contacts 3. This structure tends to invite a shortage of synthetic resin at a thin-wall section in a case where the thickness of housing 1 is reduced, so that it is difficult to further downsize housing 1 or reduce the thickness of housing 1.